1. Field of the Invention
The invention relates to portable computers having built-in AC adapters and, more particularly, to a built-in AC adapter positioned in a main chassis portion of a portable computer and having a space efficient electromagnetic interference filter incorporated therewith.
2. Description of Related Art
Portable, battery-powered computers have become increasingly popular in recent years due to their light weight and small size that permit them to be easily hand-carried in an ordinary briefcase and used by business travelers in cramped spaces lacking electrical plug-in facilities, for example, airline seat back trays. In fact, a particularly small type of portable computer, the notebook computer, which enjoys widespread popularity today is generally characterized by dimensions of 8.5".times.11" and a weight of less than 8 pounds. More recent developments in computer miniaturization have resulted in so-called "subnotebook" computers having still smaller dimensions and even lower weights.
The modern portable computer is typically comprised of a pivoting display screen portion and a main chassis portion in which a keyboard, both hard and floppy disk drives, and possibly other components, for example, a modem or PCMCIA slot, are incorporated. Also provided on the main chassis portion is at least one port for coupling the portable computer to a peripheral device, for example, a printer. Thus, the portable computer is a fully self-contained computer system suitable for use, for at least short periods of time, in situations and locations in which the use of a much larger desktop computer is simply not feasible.
As is well-known, however, even state-of-the-art portable computers have certain limitations and disadvantages when compared to their much larger desktop computer counterparts. One principal disadvantage is that portable computers are battery-powered and thus are operable only when the battery is sufficiently charged. Fortunately, however, almost all battery-powered portable computers are sold with an AC adapter. When plugged into an AC main or other convenient source of AC power, the AC adapter converts the power into a form usable by the portable computer. The AC adapter includes a line cord that plugs into the AC power source and an adapter cord that plugs into a designated power supply port, typically located on a back side portion of the main chassis of the portable computer. Power conversion is performed in a power supply coupled between the line cord and adapter cord and housed in a power supply chassis which is separate from the main chassis.
There are historical reasons for the power supply being housed in a separate power supply chassis. Because of notoriously tight volumetric constraints in the main chassis of a portable computer, the components and subsystems thereof have, for years, been the subject of constant, extensive design work directed toward making such components and subsystems as small as possible. Because the main chassis has always been fully occupied with necessary components and subsystems, there was no motivation to attempt to fit in less vital subsystems, such as the power supply. Thus, because prior art power supplies have been entirely external to the portable computer, they were never subjected to the intense miniaturization effort otherwise applied to the portable computer.
Accordingly, the various components of the external power supply have remained relatively bulky. For example, power supplies typically include heat-producing components which require heat sinks to dissipate generated heat before the accumulated heat can damage nearby electronic devices. In the past, such heat dissipation was accomplished by physically mounting thermally conductive structures having bulky and heavy fins or projections to the heat-producing components. Thus, for these and other reasons, such prior art external power supplies have been large, heavy and cumbersome, earning them the unflattering colloquial term "brick." The bulky and clumsy "brick" stood in stark contrast to the otherwise elegant and compact design of prior art portable computers. Moreover, the external power supply has made the portable computer much more difficult to transport, thereby detracting from the ease of use of such devices.
While the relocation of the external power supply within the portable computer would solve many problems which result from the external power supply, the relatively bulky size of the power supply and the tight volumetric requirements of components within the portable computer has prevented such a relocation. To accomplish this task, not only would additional space need to be made available within the chassis of the portable computer, the power supply itself would need to undergo the same type of miniaturization effort through which the rest of the portable computer has already undergone. However, any proposed miniaturization or other reduction in size of a power supply would prove a difficult task and would likely entail an electrical redesign of the power supply in order to effect a minimization of the size of the components thereof.
In U.S. patent application Ser. No. 08/502,198 (Atty. Docket No. CMPQ-0736), filed on even date herewith and previously incorporated by reference, an internal power supply which incorporates a space efficient heat dissipation structure was disclosed. The disclosed heat dissipation structure eliminates the need for the relatively large heat sinks presently in use in external power supplies. There are, however, other internal components of the power supply which unnecessarily consume large amounts of space and which should also be the subject of size reduction efforts.
One such component is the aforementioned AC adapter. As previously stated, the function of the AC adapter is to convert high voltage AC power provided from the AC main, for example, an electrical outlet, to low voltage DC power suitable for use by the portable computer. Traditionally, the AC adapter has been located within the external power supply housing previously described herein. While it would be desirable to locate the AC adapter within the main housing chassis of the portable computer, certain design considerations has caused the AC adapter to be too large to fit within the relatively small space available within the main housing chassis.
Like all electronic devices, the AC adapter generates noise during the operation thereof. While no limits on such noise were initially imposed, to prevent noise generated by an electronic device from interfering with radio, television, navigational equipment or other devices, the FCC imposed a series of increasingly stringent regulations which limit the amount of transmitted and/or conducted noise signals which may escape from an electronic device. Accordingly, all AC adapters are equipped with an electromagnetic interference (or "EMI") filter to remove high frequency noise generated thereby. In turn, the design of an AC adapter having an EMI filter which removed sufficient noise such that the AC adapter was in compliance with FCC regulations caused the AC adapter, and certain ones of its components, specifically, the EMI filter, to become relatively large in size.
Specifically, the EMI filter is comprised of plural capacitative and inductive elements located between an AC connector and a bridge rectifier circuit of the AC adapter. Various governmental regulatory agencies, particularly in Europe, have very strict requirements for components located across a high voltage AC line. Thus, as the components of the EMI filter have traditionally been located between the AC main and the bridge rectifier circuit, they have been subject to these requirements.
More specifically, such governmental regulatory agencies typically require that a capacitor located across the high voltage AC line be a type "X" capacitor. Thus, in order to comply with this regulation, the capacitors of the EMI filter which are located between the AC connector and the bridge rectifier must be of type "X". However, type "X" capacitors are subject to stringent safety requirements which cause such capacitors to be relatively large and bulky. For example, a 0.10 .mu.F type "X1" capacitor takes up 0.118 cubic inches of space while a 0.22 .mu.F type "X1" capacitor takes up 0.192 cubic inches of space. Thus, an AC adapter having an EMI filter located between the AC line and the bridge rectifier which respectively includes as the capacitor C1 and the capacitor C2, 0.10 .mu.F and 0.22 .mu.F type "X1" capacitor, to provide the necessary amount of filtering would consume 0.31 cubic inches of space merely for the capacitors of the EMI filter alone. Such an AC adapter would likely be considered too bulky to be suitable for placement within the main chassis of a portable computer.
As all capacitor and inductor components of the EMI filter have traditionally been located between the AC main and the bridge rectifier circuit, such components have tended to be relatively large. What is needed in the art is a reduced size EMI filter suitable for use with an AC adapter portion of a power supply. If such an AC adapter were achieved, the volume of the power supply would be reduced such that the power supply could be made to fit within the confines of the main chassis portion of a portable computer system. It is, therefore, an object of the present invention to provide such a internal power supply for a portable computer.